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Influenza Surveillance in the United States
Oliver Morgan, PhD MScDivision of Emerging Infections and Surveillance Services
Dr. Lyn Finelli, Scott Epperson
Influenza Division
Centers for Disease Control and Prevention
Objectives of Influenza Surveillance
• Determine which influenza viruses are circulating; where are they circulating; when are they circulating
• Determine intensity and impact of influenza activity
• Detect unusual events– Infection by unusual viruses– Unusual syndromes caused by influenza viruses– Unusually large/severe outbreaks
Influenza Surveillance
• Responsibility for national influenza surveillance rests with CDC
• State and local public health departments are our primary partners
• Review of surveillance held in 2006 & 2007 with Council of State and Territorial Epidemiologists (CSTE)– Build a system that is useful on the local level and
builds to national level surveillance
The Five Categories of Influenza Surveillance
• Viral Surveillance• Mortality Surveillance • Hospitalization Surveillance• Outpatient Illness Surveillance• Summary of the Geographic Spread of Influenza
http://www.cdc.gov/flu/weekly/
The Five Categories of Influenza Surveillance
• Viral Surveillance– WHO (World Health Organization) and NREVSS
(National Respiratory and Enteric Virus Surveillance System) Collaborating Laboratories
– Novel influenza A virus surveillance
• Mortality Surveillance • Hospitalization Surveillance• Outpatient Illness Surveillance• Summary of the Geographic Spread of Influenza
Viral Surveillance
• Viral surveillance is the foundation for influenza control efforts– Identify changes in circulating strains
• Future vaccine strain selection• Assess current vaccine match• Identify viruses with pandemic potential
– Establish seasonality• Timing of active surveillance• Timing of influenza control activities
Virologic Surveillance in the U.S.• ~150 participating laboratories
– Specimens collected during routine patient care – Weekly reports
• # specimens tested• # positive for influenza: type, subtype, age
• Novel influenza A reporting– Made nationally notifiable condition in 2007
• WHO Collaborating Labs– ~ 85 labs– Maintained by ID/CDC– State health dept.,
universities, large tertiary care hospital labs, and DoD
– Subtype influenza A – Report age data– Send subset of isolates to
CDC for further testing
• NREVSS labs– ~ 65 labs– Maintained by DVD/CDC– Hospital labs– Report data on other
respiratory viruses– Less likely to subtype
influenza A viruses– Don’t report age data– Data incorporated into flu
surveillance since 97-98
U.S. Virologic Surveillance:Participating Labs
Viral Strain Surveillance
• WHO labs submit subset of isolates to CDC strain surveillance lab
• Detailed antigenic characterization• Sequencing of some isolates• Antiviral resistance testing
– Adamantanes - when needed– Neuraminidase inhibitors - large subset
U.S. WHO/NREVSS Collaborating Laboratories National Summary, 2008-09
0
500
1000
1500
2000
2500
3000
3500
4000
4500
40 42 44 46 48 50 52 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Week
0
5
10
15
20
25
30
35
40
45
50
55A (Pandemic H1N1)
A (Unable to Subtype)A (H3)
A (H1)A (Subtyping not Performed)
BPercent Positive
The Five Categories of Influenza Surveillance
• Viral Surveillance• Mortality Surveillance
– 122 Cities Mortality Reporting System– Influenza-Associated Pediatric Deaths
• Hospitalization Surveillance• Outpatient Illness Surveillance• Summary of the Geographic Spread of Influenza
122 Cities Mortality Reporting System
• Purpose: monitor P&I related mortality in a timely manner
• Weekly reports from vital statistics offices in 122 US cities– Total # of death certificates filed– # with pneumonia or influenza listed anywhere
• ~ 1/4 of US deaths
Pneumonia and Influenza Mortalityfor 122 U.S. Cities
Week Ending 07/04/2009
4
6
8
10
21 30 40 50 10 20 30 40 50 10 20 30 40 50 10 20 30 40 50 10 20
Surveillance Weeks
% o
f All
Dea
ths
Due
to P
&I
2007 200820062005 2009
Epidemic Threshold
Seasonal Baseline
Pediatric Influenza-Associated Mortality Reporting
• In June 2004, CSTE adopted proposal to make influenza-associated death in a person <18 yrs. a nationally notifiable condition.– Reporting began in October 2004– Data reported weekly in MMWR and FluView
Number of Influenza-Associated Pediatric Deaths by Week of Death
Week ending 07/04/2009
0
1
2
3
4
5
6
7
8
9
10
11
12
2005
-40
2005
-46
2005
-52
2006
-06
2006
-12
2006
-18
2006
-24
2006
-30
2006
-36
2006
-42
2006
-48
2007
-02
2007
-08
2007
-14
2007
-20
2007
-26
2007
-32
2007
-38
2007
-44
2007
-50
2008
-04
2008
-10
2008
-16
2008
-22
2008
-28
2008
-34
2008
-40
2008
-46
2008
-52
2009
-05
2009
-11
2009
-17
2009
-23
Week of Death
Nu
mb
er o
f d
eath
s
Deaths Reported Current Week
Deaths Reported Previous Weeks
Pandemic Influenza A (H1N1) Deaths Reported Current Week
Pandemic Influenza A (H1N1) Deaths Reported Previous Weeks
The Five Categories of Influenza Surveillance
• Viral Surveillance• Mortality Surveillance• Hospitalization Surveillance
– Emerging Infections Program (EIP)– New Vaccine Surveillance Network (NVSN)
• Outpatient Illness Surveillance• Summary of the Geographic Spread of Influenza
Hospitalization Surveillance
• Emerging Infections Program
– All ages– Lab tests as part of routine
patient care– Chart reviews
• New Vaccine Surveillance Network
– 0 – 4 year olds– Children admitted with fever
or acute respiratory illness are swabbed and tested
– Culture and PCR– Chart reviews
• Population-based surveillance for laboratory confirmed influenza related hospitalizations
The Five Categories of Influenza Surveillance
• Viral Surveillance• Mortality Surveillance• Hospitalization Surveillance• Outpatient Illness Surveillance
– U.S. Influenza Sentinel Provider Surveillance Network (ILINet)
• Summary of the Geographic Spread of Influenza
Outpatient Influenza Surveillance (ILINet)
• ~2,400 healthcare providers in 50 states
• Weekly reports
– Total # of patient visits
– # visits for influenza-like illness (ILI) by age group
• ILI = fever 100 ºF (37.8 ºC) and cough or sore throat, in absence of a known cause other than influenza
• Early, peak, and late season
Percentage of Visits for Influenza-like Illness (ILI) Reported by ILINet
Week ending 07/04/2009
0
1
2
3
4
5
6
7
40 42 44 46 48 50 52 1 3 5 7 9 11 13 15 17 19 21 23 25
Surveillance Week
% o
f V
isits
fo
r IL
I
2006-07* 2007-08* 2008-09 National Baseline
Note: There was no week 53 during the 2006-07 and 2007-08 seasons, therefore the week 53 data point for those seasons is an average of weeks 52 and 1.
The Five Categories of Influenza Surveillance
• Viral Surveillance• Mortality Surveillance• Hospitalization Surveillance• Outpatient Illness Surveillance• Summary of the Geographic Spread of Influenza
Geographic Spread of Influenza
• Weekly reports from State and territorial epidemiologists
• Assessment of overall influenza activity at state level– None, sporadic, local, regional, or widespread– Incorporates virologic and ILI data– Only system reporting state-level data
• Allows local interpretation of surveillance data
Influenza Surveillance Challenges
• Not everyone with influenza accesses healthcare
• Can’t distinguish influenza from other respiratory viruses on clinical criteria– Most cases are not tested / lab confirmed
• Volume – can’t test all respiratory cases
• Not all cases will test positive– Many cases with severe influenza-related complications
(hospitalization or death)– Timing of sample collection not optimal
• Surveillance reports must be timely
Goals of Pandemic Influenza Surveillance
1. Identify and track viruses/strains
2. Describe clinical infections
3. Determine who is affected and the severity of the pandemic
4. Detect the onset and duration of the pandemic and the geographic spread
5. Guide interventions
6. Provide information to partners
Pandemic Influenza Intervals
DAccel-eration
CInitiation
EPeak
TransmissionF
DecelerationG
Resolution
BRecognition
AInvestigation
Pandemic Surveillance Framework
• Pandemic intervals as framework• Develop interval-specific surveillance strategy based on
information we need for action• Use combinations of surveillance systems to collect the
data necessary to address the goals of surveillance for each interval
• Feasible and sustainable approach to pandemic surveillance
Interval AInvestigation
Interval AReporting Frequency
WHO & NREVSS Collaborating Laboratories
Weekly
Novel Influenza A Virus Infections Daily
122 Cities Mortality Reporting System
Weekly
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Bi-Weekly
New Vaccine Surveillance Network Bi-Weekly
State and Territorial Epidemiologists Report
Weekly
Sentinel Provider Surveillance Network
Weekly
Aggregate case reporting NR
DC E F G
BA
Triggers Identification of human cases of novel influenza A
Federal Actions Maintain surveillance Support investigation/containment Characterize viruses
Interval BRecognition
Interval BReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Daily
Novel Influenza A Virus Infections Daily
122 Cities Mortality Reporting System (web-based)
Daily
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Bi-Weekly
New Vaccine Surveillance Network Bi-Weekly
State and Territorial Epidemiologists Report
Weekly
Sentinel Provider Surveillance Network (subset)
Daily
Aggregate Case Reporting NR
Triggers Confirmation of human cases and demonstration of efficient and sustained human to human transmission
Federal Actions Maintain surveillance Deploy responders Evaluate case fatality ratio and PSI
DC E F G
BA
Interval CInitiation
Interval CReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Daily
Novel Influenza A Virus Infections Daily
122 Cities Mortality Reporting System (web-based)
Daily
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Weekly
New Vaccine Surveillance Network Weekly
State and Territorial Epidemiologists Report
Daily
Sentinel Provider Surveillance Network (subset)
Daily
Aggregate Case Reporting NR
Triggers Laboratory confirmed human cases detected in any state
Federal Actions Maintain surveillance Conduct lab confirmation and characterize viruses Deploy responders/SNS Evaluate case fatality ratio and PSI
DC E F G
BA
Interval DAcceleration
Interval DReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Daily
Novel Influenza A Virus Infections Daily-NR
122 Cities Mortality Reporting System (web-based)
Daily
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Weekly
New Vaccine Surveillance Network Weekly
State and Territorial Epidemiologists Report
Daily
Sentinel Provider Surveillance Network (subset)
Daily
Aggregate Case Reporting Daily
Triggers Multiple laboratory confirmed cases in a state without epi-link
Federal Actions Maintain surveillance Conduct lab confirmation and characterize viruses (targeted) Studies of clinical course Evaluate case fatality ratio and PSI
DC E F G
BA
Interval EPeak Transmission
Interval EReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Daily
Novel Influenza A Virus Infections NR
122 Cities Mortality Reporting System (web-based)
Daily
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Weekly
New Vaccine Surveillance Network Weekly
State and Territorial Epidemiologists Report
Daily
Sentinel Provider Surveillance Network (subset)
Daily
Aggregate Case ReportingDaily-Weekly
Triggers >10% specimens submitted from states + for pandemic strain
Federal Actions Continue virologic characterization Maintain surveillance Transition to surveillance for mortality and syndromic disease
DC E F G
BA
Interval FDeceleration
Interval FReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Daily
Novel Influenza A Virus Infections NR
122 Cities Mortality Reporting System (web-based)
Daily
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Weekly
New Vaccine Surveillance Network Weekly
State and Territorial Epidemiologists Report
Daily
Sentinel Provider Surveillance Network (subset)
Daily
Aggregate Case ReportingDaily-Weekly
Triggers <10% specimens submitted from states + for pandemic strain
Federal Actions Continue virologic characterization Maintain surveillance for mortality and syndromic disease
DC E F G
BA
Interval GResolution
Interval GReporting Frequency
WHO & NREVSS Collaborating Laboratories (subset)
Weekly
Novel Influenza A Virus Infections NR
122 Cities Mortality Reporting System (web-based)
Weekly
Influenza Associated Pediatric Mortality
Daily
EIP Influenza Surveillance Network Weekly
New Vaccine Surveillance Network Weekly
State and Territorial Epidemiologists Report
Weekly
Sentinel Provider Surveillance Network (subset)
Weekly
Aggregate Case Reporting Weekly-NR
Triggers <1% specimens submitted from states + for pandemic strain during a two-week period
Federal Actions Return to routine virologic testing Maintain surveillance for mortality and syndromic disease
DC E F G
BA
Pandemic Surveillance
DAccel-eration
CInitiation
EPeak
TransmissionF
DecelerationG
Resolution
BRecognition
AInvestigation
Rapid spread within a jurisdiction Multiple lab-confirmed cases w/o an epi link
?
Surveillance Realities
• Few hospitalizations and deaths– Rethink our strategy
• Mild to moderate clinical illness
• Age distribution of cases and persons hospitalized similar to that of seasonal H1N1
Surveillance Realities
• Needed to re-focus surveillance– ILINet has been our lifeline to influenza activity
– Aggregate reports and line listed data• Limited by testing practices
– Need for information about burden of illness and clinical spectrum• Community Household Surveys
– Need for information about what states are doing and can do• Rapid Survey of Surveillance Activities in states• ILINet, other systems, lab and testing
Surveillance Planning
• Dynamic situation– Information requirement modulated by
• pandemic interval• severity of illness• planning public health interventions (vaccine, hospital surge,
stockpile)• hypothesized “mixed” season with 5 viruses circulating• hypothesized increase in transmissibility of the virus
Surveillance Planning
• Summer– Option 1 Current Strategy
• Weekly aggregate reporting• ILINet (subset)• Automated syndromic systems• WHO/NREVSS daily (subset)
– Option 2 Scale back• D/C weekly aggregate reporting (states post case counts?)• ILINet Weekly• WHO/NREVSS weekly
Surveillance Planning
• Fall– Option 1 Continue Current Summer Strategy
• Weekly aggregate reporting• ILINet daily (subset)• Automated syndromic systems (BioSense, etc)• WHO/NREVSS daily (subset)
– Option 2 Scale Up• Return to daily line listed case reporting or web based CRF
– Staggered reporting of CRF• Hospitalization case reporting (long or shorter form)
– First “200” or EIP if widespread• Other systems daily
Next steps
• Convene CSTE working group comprised of state Epidemiologists and surveillance coordinators
Additional Information
• CDC/Influenza Division FluView surveillance report– Weekly from October through mid-May– http://www.cdc.gov/flu/weekly/fluactivity.htm
• General influenza information– http://www.cdc.gov/flu/
• Avian influenza information– http://www.cdc.gov/flu/avian/
• Pandemic influenza– http://www.pandemicflu.gov/
West SouthCentral - 7
Pacific - 9
Mountain - 8West NorthCentral - 4 East North
Central - 3 Mid Atlantic - 2
New England - 1
South Atlantic - 5
East South Central - 6
Pacific - 9
Influenza Surveillance Regions
Number of Specimens Tested for Influenza and Number Positive
Season All labs
# tested # positive
2002-03 96,871 9,841
2003-04 152,262 25,104
2004-05 186,478 24,501
2005-06 180,961 21,497
2006-07 189,415 23,941
2007-08 * 235,436 40,167
*data as of July 18, 2008
National Center for Health Statistics Mortality Data
• Provides a complete and more detailed record of cause of death
• > 99% of all deaths in the US• Separate record for each individual
– Basic demographic data– Date of death– Underlying & contributing causes of deaths
• Data used for special studies – Mortality estimates obtained from mathematical modeling
• Not available until ~ 2 yrs later
Growth of the Influenza Sentinel Physician Surveillance System
0
500
1000
1500
2000
2500
3000
1996-97 1997-98 1998-99 1999-2000
2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08
Season
En
roll
ed P
hys
icia
ns
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
20000000
Pat
ien
t vi
sits
enrolled physicians regularly reporting physicians patient visits
*
* As of 7/18/2008
Percentage of Visits for ILI Reported by Sentinel Providers,National Summary, 1997-98 – 2007-08
0
1
2
3
4
5
6
7
8
19
97
-40
19
97
-50
19
98
-07
19
98
-17
19
98
-46
19
99
-04
19
99
-14
19
99
-43
20
00
-01
20
00
-11
20
00
-40
20
00
-50
20
01
-08
20
01
-18
20
01
-47
20
02
-05
20
02
-15
20
02
-44
20
03
-02
20
03
-12
20
03
-41
20
03
-51
20
04
-09
20
04
-19
20
04
-48
20
05
-06
20
05
-16
20
05
-45
20
06
-03
20
06
-13
20
06
-41
20
06
-51
20
07
-09
20
07
-19
20
07
-47
20
08
-05
20
08
-15
Week
% o
f V
isits fo
r IL
I
99-00 00-01 01-02 02-03 03-04 04-05 05-06 06-07 07-0898-9997-98
Influenza Activity Levels
• No Activity: No laboratory-confirmed cases of influenza and no reported increase in the number of cases of ILI
• Sporadic: Small numbers of laboratory-confirmed influenza cases or a single influenza outbreak has been reported, but there is no increase in cases of ILI
• Local: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of the state
• Regional: Outbreaks of influenza or increases in ILI and recent laboratory confirmed influenza in at least 2 but less than half the regions of the state
• Widespread: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of the state
. .. ..
Current Status of WHO System
• >175,000 isolates/yr (600 to 1200 M cases)• WHO CCs receive 6,500 – 8,000 samples/yr.• WHO CCs and NICs sequence HA of 1,000
samples/yr; complete genomes now sequenced (e.g, members of GIP sequenced complete genomes of 20 H5N1 viruses in few weeks)
• >290 M doses of influenza vaccine w/wide
2007-08 Surveillance Summaries
U.S. WHO/NREVSS Collaborating Laboratories National Summary, 2007-08
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
40 42 44 46 48 50 52 2 4 6 8 10 12 14 16 18 20
Week
Nu
mb
er
of I
sola
tes
0
10
20
30
40
50
Pe
rce
nt P
osi
tive
A(H3)
A(H1)
A(Unsubtyped)
B
Percent Positive